The name is absent

142

Fast Settle Feature of the NSA

Fortunately when the NSA was designed, the responsible engineer (Shane
Guillory) predicted that at some point a device for concurrent stimulation and recording
would be implemented. As a result he included a fast settling switch that when
activated bypasses an RC loop that is used for filtering, providing a shunt for a capacitive
charge. This switch can potentially be controlled by software, but since this feature has
never been used before that software has not yet been written. To test if the fast settle
switch can be used to reduce the recording latency I disconnected the input from the
FPGA that controls it on one of the WERM boards of an NSA, and soldered it to a wire
that extended outside of the NSA case. The fast settle feature could then be turned on
and off by applying 5V or grounding the wire.

The result is shown in figure 6A below. As can be seen in the figure the latency
has been virtually eliminated. Figure 6B shows the recording at maximum temporal
resolution which reveals the latency to be ~3.5ms. This was repeated with different
waveforms and the latency was consistently 3.5ms. However, as can also be seen in
figure 6A the stimulus waveform is now being recorded when the Stim Project is set to
stimulate. This could be the result of one of two things: it could be another instance the
cross-talk issue that we saw previously; or it could be that the switches are not
switching properly, or are leaky when open, which would be a severe problem. To test
this all switches were tested using a multimeter under the same conditions of the

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